36 watts will be fine for most designs. Actually, around ten watts would probably be enough for what most people are using. I believe Wayne recommends his resistor values assuming you intend on running a great deal of power through your speakers, like 300-400 watts. If you are running yours with around 100 watts - which is plenty - you only need perhaps 20 watt resistors in your CD crossover.

The impedance compensation is a little different. You should try to keep the wattage value as high as you can, but this isn't as much of a problem. You can use the dummy load resistors from PE which are 100 watts or even 200 watts in 4 ohm or 8 ohm models.

As far as resistor tolerances go, I personally think within 10% of the intended value is acceptable and not noticable, although some people might disagree. I aim for the closest possible numbers, but I won't lose any sleep using a 9 ohm resistor when it should be 10 ohm, or whatever. 15 instead of 16 and 25 instead of 27 is a very acceptable tolerance, no worries.

As for square ports, they will work just as well as round. In fact, some others have used square ports on four pi's, and Wayne's PiAlign gives you the choice of square or round ports. I think he just doesn't do it because it's not worth the trouble when you can easily use a prefab'd round port.

Hope I covered everything.

Adam